Shigella organisms are a group of Gram-negative enteric bacilli that cause acute bacillary dysentery in humans. The signature feature of this disease is exhibited by an intense inflammatory reaction manifested clinically as passage of bloody stools. Humans and some non-human primates, namely Old World monkeys in Africa and Asia serve as the only hosts that are naturally susceptible to Shigella infection. The relationship between Shigella and the human intestinal epithelium and the subsequent inflammatory response, which determines clinical virulence, is undoubtedly complicated and relatively little information is known pertaining to this process. We have identified key components of the Shigella-host relationship that may explain some of the host adaptation exhibited by this organism, in addition to strategic mechanisms underlying Shigella flexneri pathogenicity. First, we have previously demonstrated that S. flexneri has evolved the ability to regulate functional components of the epithelial tight junctional complex following early interactions at the apical pole of model intestinal epithelia. Second, we have recently demonstrated a critical role for the eicosanoid hepoxilin A3 (HXA3) in the transepithelial migration of neutrophils induced by S. flexneri. HXA3 is a derivative of arachidonic acid formed from the enzymatic action of the 12- lipoxygenase (12-LO) pathway. Our targeted approaches will test the hypothesis that specific host-Shigella interactions that lead to the release of HXA3 will provide novel therapeutic intervention strategies for the treatment of shigellosis. At the same time much information will be learned about the immunology of mucosal surfaces as well as the underlying mechanisms of S. flexneri pathogenesis. Thus, the long-term goal of this project is to understand the molecular mechanisms underlying S. flexneri-intestinal epithelial interactions that lead to acute infectious colitis. The specific aims of this proposal are ultimately aimed at achieving this goal and are three-fold: Specific Aim 1 is focused on how Shigella invade and is designed to understand the molecular mechanisms by which S. flexneri regulates the intestinal epithelial tight junctional complex. Specific Aim 2 will determine the molecular mechanisms by which the S. flexneri Outer surface proteins (Osp), virulence factors that are involved in regulating inflammatory pathways, engage transcellular signals underlying PMN recruitment, and hence HXA3 secretion. Lastly, in Specific Aim 3 we will develop a novel therapeutic intervention strategy, using an in vivo model of shigellosis for the treatment of shigellosis. In view of the fact that Shigella is a major cause of diarrhea and mortality worldwide, validates the study of Shigella pathogenesis for potential therapeutic drug development especially given the increase in antibiotic resistance and the lack of an efficacious vaccine.